11 Tips for Fertilizing Your Garden this Spring

As your garden awakens from the chill of winter, it’s the perfect time to nourish your plants in preparation for an abundant season. Fertilizing your garden isn’t rocket science, but it does require proper timing and attentiveness to help you avoid critical mistakes.

Plants growing in poor, low-nutrient soils may fail to produce a yield or become more susceptible to pests and diseases. On the other hand, over-fertilized plants can become extremely stressed, making them vulnerable to yellowing leaves, shriveled roots, defoliation, and sometimes crop failure. 

For flowering and aromatic plants, too much fertilizer can decrease the amount of blooms and reduce the fragrant oils produced by the plant. But for some vegetables and fruiting annuals, a lack of fertilizer can prevent the plant from yielding altogether. As you can tell, balance is the key to success with spring fertility. 

Let’s dig into 11 spring fertilizing tips to provide your garden with all the nutrients it needs without going overboard.

11 Tips for Fertilizing Your Garden this Spring

The vitamin and nutritional needs of each person are never the same, and plants are equally unique. Not all fertilizers are created equal, and not all plants need the same nutrients. Before you start pouring fertilizer around your garden, remember to check the ratios and amounts of each specific nutrient. Here is a quick refresher on fertilizer labels:

Use the following 11 simple tips to deliver the right forms and amounts of these nutrients to different types of plants. When in doubt, air on the side of “less is more.” You can always add more fertilizer later, but it is more difficult to remove it.

Observation and Timing Matter

The best time to fertilize a plant depends on its stage of growth. To master the timing of your fertilizer applications, use these rules of thumb and general observations:

Most established landscaping trees and native shrubs do not require fertilizer. Notice if a plant has robust growth from last season, such as deep green leaves, lots of new branches, and a strong central trunk. These are clues that the plant has sufficient nutrients from the native soil.

Prioritize Balanced, Slow-Release Fertilizers

Balanced, slow-release fertilizers are typically the best option for home gardeners because they deliver even amounts of nutrients to your plants, and they last a long time in the soil. Balanced means the NPK ratios are close in number, for example, 4-5-5 or 10-10-10. If the ratio is extremely skewed toward one nutrient, it can make fertilizing more complex and potentially cause imbalances or deficiencies in plant growth.

Slow-release products like Espoma Garden-Tone Organic Plant Food provide an expertly crafted blend of nutrients that can fuel your plants for most of the season. Because it is granular, it’s easy to mix a handful into your seed-starting mix or planting holes.

Organic fertilizers like compost, feather meal, bone meal, and aged manure are slow-release because they require soil microorganisms to help break them down. These nutrients interact with your soil to gradually become available to plants over time. This is why spring applications are so important; the plants can uptake the available nutrients as needed without getting overwhelmed by a megadose of fertilizer all at once.

There is also less risk of fertilizer burn when using these types of products. Quick-release synthetic fertilizers may overdose your plants with certain nutrients like nitrates, causing serious issues like leaf drop, slow growth, or plant death. If you’re worried about overfertilization or nutrient leaching into nearby waterways, choose slow-release organic fertilizers.

Understand Heavy, Medium, and Light Feeders

Every plant and variety has different needs, but some generalizations are made to help gardeners group similar plants together. You may have heard the terms “heavy, medium, or light feeders.” This refers to whether a plant needs a lot of fertilizer (for example, tomatoes) versus a plant that can subsist with lower amounts of fertility (such as carrots).

Heavy feeders include:

• Tomatoes: These famous garden plants demand substantial nutrition to support continuous fruit development throughout the season. Be sure to choose a fertilizer with a balance of NPK to fuel fruit growth without causing an overgrowth of leaves.
• Corn: Fast-growing and tall, corn rapidly eats up soil nutrients and likes lots of fertility.
• Squash: With their huge, rambling vines and massive fruits, it should come as no surprise that squash-family crops require ample nutrients for robust growth.
• Brassicas: Most cole-family crops like cabbage, broccoli, cauliflower, and Brussels sprouts need a lot of soil fertility to yield large, dense heads.
• Giant Vegetables: Artichokes, rhubarb, melons, and pumpkins need plenty of NPK and micronutrients to produce their huge leaves and fruits.

Medium feeders include:

• Fruit Trees: Once established, most fruit trees are moderate feeders that enjoy a diluted dose of all-purpose fertilizer each season. 
• Peppers: While they don’t demand as much nutrition as tomatoes, peppers still need balanced soil fertility to fuel the continuous production of ripe fruits throughout the summer.
• Lettuce: Leafy greens have moderate nutrient requirements but can suffer if over-fertilized.
• Chard: A balanced blend of micronutrients and NPK is important for these rainbow plants to supply leaves all season long.
• Beets: These plants need moderate levels of fertility and are sometimes subject to boron deficiency, which can cause black spots.

Light feeders include:

• Herbs: Fragrant herbs like cilantro, dill, mint, sage, thyme, rosemary, and lavender are all light feeders that perform best in less fertile soils. In the next section, we’ll explain why too many nutrients can actually reduce the flavor and scent of these herbs.
• Native Plants: Native species do not typically need supplemental fertilization unless they are grown in containers.
• Wildflowers: Most wildflowers thrive in poor soils and do not require additional fertilizer.
• Beans and Peas: Legume-family crops have a symbiotic relationship with nitrogen-fixing bacteria in the soil. In other words, they can make their own fertilizer and don’t typically require supplementation.

These classifications are especially useful for companion planting and crop rotations. When choosing companion plants, you can simplify your fertilization processes by growing crops with similar needs in the same area. For example, cauliflower and broccoli both require lots of nutrients, making them good comrades in an extra fertile bed. In the context of crop rotation, you may plant a medium-light feeder like lettuce in the bed where you grew tomatoes last year.

Don’t Add Too Much Nitrogen to Certain Plants

Over-fertilizing is one of the biggest mistakes made by beginner gardeners. In particular, excessive amounts of nitrogen can cause some major disappointments in the garden, such as leggy growth, lack of fruits, lack of flowers, and reduced flavor or aromatics. 

Nitrogen is a vital plant nutrient to support verdant green leaves and lots of new shoots that are rich in chlorophyll. Chlorophyll is the key green pigment that plants use to create their own food in the process of photosynthesis. However, when a plant receives too much nitrogen, it causes an excessive amount of leafy foliar growth at the expense of other plant parts. 

Too much nitrogen causes reduced fruit, reduced flowers, and/or reduced fragrance in these types of plants:

Reduced Fruit

For fruiting plants like tomatoes and squash, too much nitrogen causes an overgrowth of rich green leaves. Overfertilized plants can grow outrageously large and bushy, which can cause overcrowding and disease issues. The stems may be leggy and weak, potentially collapsing. Worse, when the warmest months arrive, these plants often fail to produce flowers or fruits because the excessive nitrogen has signaled to the plant to keep growing more leaves.

Reduced Flowers

For flowering plants like roses and rhododendrons, too much nitrogen also causes an explosion of foliar growth at the expense of blooms. You may not experience as many gorgeous flowers if your plant puts all its energy into leaf growth.

Reduced Fragrance

For aromatic plants like lavender or rosemary, excess nitrogen reduces the concentration of essential oils in the leaves and blooms. This means that your favorite-smelling plants may have reduced fragrance or none at all.

The best way to avoid adding too much nitrogen to these species is to use a balanced, slow-release organic fertilizer like those explained above. Avoid fertilizers with high ratios of nitrogen and low amounts of other nutrients (i.e., 10-0-0 or 20-1-0) unless you are certain that the soil is extremely deficient in nitrogen. When in doubt, apply less than you think you need, or dilute your fertilizers!

Water Consistently

Fertilizers are difficult for plants to uptake in dry soils. Always water after you apply fertilizer. Particularly when using organic granular fertilizers, it is important to irrigate to help solubilize the minerals and transport them down toward the roots. Once the particles reach deeper in the soil, microbes can get to work breaking down the nutrients so they are accessible to plants.

Watering schedules vary widely based on your soil, climate, and plant species. As a general rule of thumb, check the soil moisture before fertilizing to assess how much water you’ll need to add. 

Stick your finger four to six inches into the soil. If your skin comes out clean, the soil is likely dry. Mix in your granular fertilizer and then water right away. 

If your skin comes out wet or caked in dirt, the soil is probably too soggy. You can wait for it to dry out or just apply the fertilizer and let it be. The ideal soil moisture for most plants is about the wetness of a wrung-out sponge. This ensures that nutrients can dissolve into the soil without suffocating the roots.

However, if you are using a concentrated liquid fertilizer, wait a couple of hours before watering. You don’t want to leach the fertilizer out of the soil before plants have had a chance to absorb it.

Mix Fertilizer into the Soil Surface

Plants don’t absorb fertilizer at the soil surface; they uptake it through their roots! It’s best to mix granular fertilizers into the top few inches of soil at the beginning of spring. You don’t want to leave fertilizer exposed on top of the bed where it is subject to blowing away, washing away, or getting eaten (see my dog story below!) 

You can use a gloved hand to gently scratch the soil surface as you sprinkle your fertilizer in place. Better yet, add the fertilizer into the planting hole before transplanting. You can also mix a certain measurement of granules into the top inches of your garden soil before direct seeding. 

Don’t get me wrong, fertilizer left on the soil surface will eventually reach the plant roots as it is exposed to rain and irrigation. However, it is faster and more effective to mix the fertilizer into the soil so it stays where you want it.

Add Mulch

Organic mulch, like leaves or straw, is like garden gold. It suppresses weeds, moderates soil temperature, and prevents the soil from drying out in the spring and summer sun. If you are already in the garden adding fertilizer, you might as well use the opportunity to apply mulch. 

Spreading mulch around your perennials after fertilizing is especially useful for improving soil quality, retaining moisture, and maintaining an attractive yard. In annual beds, you can apply mulch after you scatter fertilizer and plant your seedlings. This will help them get established more quickly.

If mulch is already in place, you can apply fertilizer on top of the mulch. However, in windy climates or backyards with pets, I recommend fertilizing beneath the mulch. Many organic fertilizers are attractive to animals. My dogs go crazy for stinky bone meal or feather meal fertilizers, and it makes them smell horrific. I’d prefer for my plants to absorb the nutrients before the dogs eat it!

The mulch helps keep the fertilizer in place so it doesn’t blow away in the wind or get eaten by a hungry critter.

Dilute, Dilute, Dilute!

Do not apply concentrated fertilizers directly to your plants! A megadose of nutrients can severely stress a plant or even kill it. Whether you’re using an organic fish emulsion fertilizer or a concentrated synthetic fertilizer, dilution is essential. 

It is rare to find fertilizer products that can be poured straight out of the container. Most products are concentrated and include specific instructions on the label for diluting with water.

Use labeled measuring cups specially reserved for your fertilizers to avoid cross-contamination with your kitchen. The easiest way to dilute fertilizer is to use a designated watering can or bucket to pour in the concentrate and mix it with the recommended amount of water.

Avoid Applying Raw Manure

While manure is an excellent source of plant nutrients and organic fertility, it is recommended to age or compost manure before adding it to your garden. Raw manure is, after all, animal poop. It can harbor unwanted pathogens and disease-causing bacteria. Moreover, raw manure can have higher amounts of nutrients that may cause symptoms of fertilizer burn on young plants. For these reasons, I never apply raw manure to my garden beds, especially in areas with new transplants or seeds.

Aging involves simply leaving a pile of manure at the corner of your garden to break down for a few months. This passive method promotes microbial breakdown of the nutrients so they are less intense on your plants, which can be particularly helpful for high-nitrogen manures like chicken poop.

Even better, you can compost manure by blending it with a carbon-rich material like leaves. A ratio of four parts leaves to one part manure can yield excellent compost that heats up to a sufficient temperature to kill any pathogens inside. As long as you flip the pile to maintain aeration, you can transform your manure into an even better compost amendment within a few weeks.

Test Your Soil

If you want to be extra precise about your fertilizer applications, test your soil in the spring as soon as the ground has thawed. Soil tests will tell you the overall mineral composition of the soil, but it’s also important to recognize that many of the readings are only a snapshot in time. 

Highly “mobile” plant nutrients like nitrogen are constantly changing based on water, temperature, and other factors. So, a nitrogen reading on your soil test may not be the same a few weeks down the line. On the other hand, soil-immobile nutrients like potassium or phosphorus tend to stay the same over time, which means the soil test reading is more reliable.

For gardeners who use synthetic quick-release fertilizers, soil chemistry information can be very useful. But if you are an organic, ecologically-focused gardener, soil tests are a bit more finicky. The biology of a garden ecosystem is always changing because your soil is full of microorganisms that are breaking down organic matter and mineralizing nutrients at all times. Test each year with an easy-to-understand and perform soil test kit.

Fertilize Houseplants

Indoor gardeners should also be fertilizing houseplants in the spring. Although your lovely succulents and tropical species are not exposed to the outdoor winter, they naturally react to the amount of light through your windows. Many house plants go dormant or barely grow during winter. As they awaken in the spring, a dose of fertilizer can help them take off. 

March or April is a great time to start fertilizing indoor plants. The type and quantity of fertilizer are highly dependent on the plant species and size, so be sure to reference specific growing guides. 

If you are up-potting or transplanting houseplants in the spring, this is the perfect opportunity to mix in granular slow-release fertilizer. If applying a liquid fertilizer, carefully dilute. It’s often better to dilute even more than the label recommendation because of the confined soil environment of a pot or indoor container.